We started to lose search referral traffic around the same time that I moved some of our sitemaps to a subdomain. Could this have hurt us?

I followed Google's steps to creating a sitemap under a different subdomain. The new sitemaps.foo.com subdomain is being crawled and indexed well.

Both www.foo.com and sitemaps.foo.com have been verified in Google Webmaster Tools. They appear as distinct sites. Is this correct? I can't find a way in Webmaster Tools to say "Hey, sitemaps.foo.com is really owned by www.foo.com, so show them together and make sure to attribute sitemaps.foo urls to www.foo"